President Trump's latest threat of 50% tariffs on Canadian steel and aluminum upended markets Tuesday, but his plan for an increase of any level could be heartily welcomed by American manufacturers of those products.

"We stand fully behind your leadership," nine US steel industry executives said in a recent letter to the president about a set of 25% duties planned on all steel and aluminum imports from all countries set to come into force tomorrow.

Trump surprised markets on Tuesday by announcing that he would by going higher and imposing "an ADDITIONAL 25% Tariff, to 50%," on steel and aluminum from Canada on top of the previously announced 25% duties that start Wednesday.

He then suggested later in the day that those tariffs may not happen after Ontario's premier said it would suspend a surcharge on exports of electricity.

"I'll let you know," Trump told reporters as Philip Bell, the Steel Manufacturers Association president, added in a live Yahoo Finance interview Tuesday afternoon that he hopes at least the 25% duties stay in place.

Stocks quickly sold off Tuesday morning as the president also elevated his war of words with Canada but then whipsawed up and down on the competing headlines.

Read more: What Trump's tariffs mean for the economy and your wallet

"It's more uncertainty, it's more chaos, he changes his mind on a whim," Slatestone Wealth chief market strategist Kenny Polcari said in another Yahoo Finance live appearance at one point.

But Tuesday morning's fresh round of agita belies a more nuanced view of Trump's 25% duties within the steel and aluminum industry after years of executives expressing concern about things like "steel dumping" from China.

And there is now bipartisan ire about subsidized Chinese steel undercutting world markets, leading many CEOs in the sector to actively cheer on Trump's most protectionist impulses.

Executives also have a familiar legal and political playbook for this week's steel and aluminum tariffs after Trump undertook similar actions during his first term — even though the duties do represent a mixed bag for some with closer economic ties to Canada.

One example of the industry support for Trump has come in the form of the recent letter sent to the president from the heads of US Steel (X), Nucor (NUE), and Cleveland Cliffs (CLF), among others, touting the plan for 25% blanket duties.

"We urge you to resist any requests for exceptions or exclusions and to continue standing strong on behalf of American steel," the letter said, according to a copy reviewed by Yahoo Finance.